1. Field of the Invention
The present invention relates to an exchange-coupled film utilizing exchange coupling between an antiferromagnetic layer and a ferromagnetic layer, and a magnetic sensing element including the exchange-coupled film.
2. Description of the Related Art
FIG. 8 is a sectional view of a magnetic sensing element (spin-valve thin-film element) having a conventional structure. The magnetic sensing element includes a multilayer film M exhibiting a magnetoresistance effect, and hard bias layers 109 and electrode layers 110 disposed at both sides of the multilayer film M. The multilayer film M includes a seed layer 103, an antiferromagnetic layer 104, a pinned magnetic layer 105, a nonmagnetic layer 106, a free magnetic layer 107, and a protective layer 108 disposed in that order from the bottom. The magnetization of the pinned magnetic layer 105 is pinned in the height direction (in the Y direction in the drawing) by an exchange coupling magnetic field generated at the interface between the antiferromagnetic layer 104 and the pinned magnetic layer 105. In general, the antiferromagnetic layer 104 is composed of PtMn or IrMn, and the pinned magnetic layer 105 is composed of CoFe. The hard bias layers 109 are in contact with both sides in the track width direction (in the X direction in the drawing) of the multilayer film M and apply a longitudinal bias magnetic field to the free magnetic layer 107 so that the magnetization of the free magnetic layer 107 is aligned in the track width direction. The electrode layers 110 are conductors that supply a sensing current to the multilayer film M. The sensing current from one of the electrode layers 110 mainly flows through three layers, i.e., the pinned magnetic layer 105, the nonmagnetic layer 106, and the free magnetic layer 107. The magnetic sensing element having such a conventional structure is disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 9-237716, p. 7, FIG. 10), Patent Document 2 (Japanese Unexamined Patent Application Publication No. 9-148132, p. 8, FIG. 10), or Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2002-208120, p. 11).
Patent Documents 1 to 3 each describe a magnetic sensing element in which an antiferromagnetic layer composed of IrMn and a pinned magnetic layer (ferromagnetic layer) composed of CoFe are disposed on each other. However, with respect to the composition ratio of CoFe, only Co90Fe10 is described. When a pinned magnetic layer composed of Co90Fe10 and an antiferromagnetic layer composed of PtMn are disposed on each other, the exchange coupling magnetic field produced at the interface between the pinned magnetic layer and the antiferromagnetic layer is sufficiently strong, and the magnetization of the pinned magnetic layer can be strongly pinned. However, when such a pinned magnetic layer and an antiferromagnetic layer composed of IrMn are disposed on each other, the exchange coupling magnetic field produced at the interface between the pinned magnetic field and the antiferromagnetic layer is weak, and there may be a possibility that the magnetization direction of the pinned magnetic layer is reversed during the fabrication process of the magnetic sensing element. In particular, in a top spin-valve magnetic sensing element in which an antiferromagnetic layer is disposed on a pinned magnetic layer, there is a high probability of magnetization reversal of the pinned magnetic layer.